https://twitter.com/bz_moz/status/751424738279452673 links to https://jsfiddle.net/76vqay5e/, which has a test case that repeatedly creates and destroys iframes.

On my Z620, the fiddle reports ~20ms per loop in Chrome. In Firefox, it's ~1ms per loop.

I added some random tracing to WindowProxy initialization: https://codereview.chromium.org/2131273002

~5.5 ms is spent in WebLocalFrameImpl::createChildFrame. Only 0.5ms is spent in the sync IPC call: something else here is accounting for the majority of time.

~12.5 ms is spent in WindowProxy::initialize.
  - About half that is spent in v8::Context::New
  - The other half is spent updating the document, activity logger, security token
    - 2.5 ms of that is spent in didCreateScriptContext, which is a hook for extensions